Electrical circuit apparatus for detecting when the current which normally produces an arc between electrodes takes a different path



NOV. 3, 1970 KEMENY ETAL 3,538,378

' ELECTRICAL CIRCUIT APPARATUS FOR DETECTING WHEN THE URRENT WHICH NORMALLY PRODUCES AN ARC BETWEEN ELECTRODES TAKES A DIFFERENT PATH Filed June 13, 1967 I 3| 60 OR ZI Ll 33 .f CONTROL F lG.l.

37 I 40 3 ARC 0.c. HEATER SOURCE 4| i ALARM 39 OR CONTROL F IG.2.

WITNESSES G uxsmons d I r I eorge emenyon Armin Bruning.

' .ATTORNEY United States Patent U.S. Cl. 315-411 27 Claims ABSTRACT OF THE DISCLOSURE In an arc heater the arc current normally produces an are between electrodes. However, the arc current may suddenly fake a path through deposited carbon or some other conductive material deposited on the wall or heat shield of the arc chamber resulting in an electrically conductive path between the arc heater electrodes. As a result the arc goes out. Furthermore, due to the failure of electrical insulation, the arc current may take a path through the arc heater structure. Electrical circuit means is provided, electrically connected across the electrodes and across the source of potential producing and sustaining the are, for detecting the absence of high frequency voltage variations which are normally present while the arc is taking place between electrodes. These high frequency are voltage variations occur whether the arc is sustained by direct or alternating current. We rectify the high frequency components and utilize the signal obtained by rectification to operate a warning relay or other warning device which may shut off the current when the high frequency component is absent. Where direct current sustains the are we also provide relay circuit opening or warning means which operates when the high frequency voltage component stops. Where an alternating current source produces the arc, we employ a filter which substantially eliminates the power frequency.

FIELD OF THE INVENTION The invention relates to apparatus for shutting off the current to an arc heater or giving a warning when the arc current, normally between electrodes, takes a current path through carbon or other electricity conducting material deposited on the walls or heat shields of the arc heater as a result of pyrolysis of a hydrocarbon gas or other cause, or takes a path through the arc heater structure because of the failure of electrical insulation.

DESCRIPTION OF THE PRIOR ART Heretofore it is believed the only known way of ascertaining when the current which normally produces an are between electrodes took a path through a carbon deposit was by monitoring the temperature of gas obtained from the arc heater or by continuous observation of the arc volt-age trace on an oscillograph instrument. The prior art methods are entirely unsatisfactory because a current path between electrodes through a carbon deposit or deposit of other conductive material can cause serious electrode damage in a very short interval of time.

SUMMARY OF THE INVENTION Where alternating current is used to sustain an are between electrodes in an arc heater, a high-pass filter is electrically connected either directly across the source or the electrodes or across a portion of a voltage divider connected across the alternating current source or the electrodes. The output of the high-pass filter is applied to a rectifier, the rectified output of which is applied to a normally energized relay winding while the arc is taking place 3,538,378 Patented Nov. 3, 1970 ice between electrodes and high frequency are voltage variations occur. Should the arc current cease to produce an arc and take any other path between electrodes, the high frequency voltage variations cease, and the relay winding becomes deenerg-ized thereby closing an alarm or control circuit.

Where a direct current source supplies the arc current, a rectifier is coupled, for example capacitor coupled, to the source of direct current or across the electrodes or to a tap on a voltage divider and the output of the rectifier ap plied to a normally energized relay which remains energized while the high frequency voltage variations are present, the relay becoming deenergized and the contacts thereof closing an alarm or shut-down circuit when the high frequency voltage variations present during normal operation cease.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electrical schematic circuit diagram of the apparatus of the invention as used with an alternating current are current source, and

FIG. 2 is an electrical schematic circuit diagram of the invention used with a direct current are power source.

DESCRIPTION OF T HE PREFERRED EMBODIMENTS In FIG. 1 an arc heater 10 which it is understood has a pair of spaced electrodes, not shown, electrically insulated from each other between which the arc takes place, is connected to an alternating current source by leads 12 and 13. The alternating current source 11 has a relatively low impedance; for example, the arc voltage may be 400 volts and the arc current may be 5000 amperes. Connected across leads 12 and 13 and accordingly connected across the electrodes is a voltage divider 14 having a tap thereon connected by way of lead 15, and also by way of lead 13, to supply an input to a high pass filter generally designated 19 including the capacitor 16 and inductor 18. The high pass filter 19 has the values of capacitance and inductance chosen whereby the filter passes only frequencies above 60 cycles per second, the frequency of source 11, or substantially eliminates the 60 cycle component or attenuates it to a very low percentage of its original value. The output of the high pass filter is applied by way of leads 13 and 17 to a rectifier 23 shown as full wave but which could be half wave of conventional design and employing any suitable rectifiers, the full wave rectifier 23 supplying its output by leads 2S and 26 to the winding 29 of a relay generally designated 28. Preferrably the winding 29 has capacitor 27 connected thereacross to prevent the relay from being responsive to momentary variations in voltage having no significance as far as the circuit is concerned, the charge on capacitor 27 also preventing winding 29 from becoming deenergized during the intervals between high frequency impulses. Relay 28 has a movable armature 30 and fixed contacts 31, these being connected by way of switch 66', leads 32 and 33 and energizing source 60 to device 61 which may give an alarm or be a relay operating suitable circuit interrupting means in one of the leads 12 and 13 for opening the circuit to the arc heater 10. It will be noted that wind ing 29 is normally energized as a result of a rectified signal obtained from normal high frequency components or variations in the arc voltage, these being passed by the highpass filter 19 and rectified by the full wave rectifier 23 and energizing Winding 29 to maintain the relay armature 30 out of contact with the contacts 31. Should the current between electrodes in arc heater 10, which normally produces an are between the electrodes, suddenly begin to follow a path through a conductive deposit on the walls and/or heat shields of the arc heater or through the arc heater structure as a result of the breakdown of electrical insulation, then the high frequency variations in the arc voltage or power supply voltage across electrodes will cease, winding 29 will become deenergized and armature 30 and contacts 31 will close a circuit therebetween. The device 61 connected to leads 32 and 33 will be energized by the energizing source means :60.

It will be understood that upon starting up the arc heater, switch 66 is open, and is not closed until the are between electrodes is established and has been running for perhaps two seconds.

It has been found in practice that the voltage between electrodes can be about the same in magnitude for an arc heater condition in which normal arcing takes place between the electrodes and for a condition where current conduction is through a carbon deposit or some other deposited conductive material. One the other hand, while the arc is taking place between electrodes, there are normally high frequency variations in the arc voltage and these normal high frequency variations in arc voltage are continually present while the arc is operating normally.

Particular reference is made now to FIG. 2. In FIG. 2 the arc heater 36 has a pair of spaced electrodes, not shown, and a wall and/ or heat shield portion between electrodes, not shown, on which carbon or some other conductive material may be deposited. Arc heater 36 is connected to direct current source 37 byway of leads 38 and 39. Leads 38 and 39 are also being connected across a voltage divider 40 having a tap connected by way of lead 41 to a coupling capacitor 42 which is connected by way of lead 43 to rectifier 46, and together with lead 39 supplies an input to the rectifier 46 shown as full wave but which may be half wave. The full :wave rectifier 46 supplies its output by way of leads 47' and 48 to the winding 51 of a relay designated generally 50 having armature 52 and stationary contacts 53. Preferably winding 51 has capacitor 49 connected thereacross. Relay 50 is normally energized while the arc in arc heater 36 is operating properly and normally, there being high frequency voltage variations in the arc voltage, these being coupled by capacitor 42 to the full wave rectifier 46 which supplies an output signal which maintains winding 51 energized while the arc heater is operating normally. In normal operation, armature 52 is not in contact with contacts 53. Should the arc current suddenly take a path through carbon or other deposited conductive material, deposited on the wall and/ or heat shield of the arc heater between electrodes, or through the structure of the arc heater because of the failure of electrical insulation, winding 51 becomes deenergized and an electrical circuit is completed through 52-53 to alarm or control means 64 connected by way of power source 63 and switch '65 to leads 54 and 55. In starting up the arc heater 36, switch 65 is open, and is closed after, for example, two seconds.

Where the sources of current 11 or 37 for the arcs are of relatively low voltage, it will be understood that the voltage dividers 14 and 40 respectively may be dispensed with.

It will further be understood that the circuitry can be utilized for detecting shorting of the are through any other electricity conducting deposits and not only for detecting shorting through carbon deposits.

It will be further understood that the circuit will also detect shorting of the arc current by any other means such as accidental shorting through any electricity conducting structural members.

It should also be noted that other means not illustrated may be provided for temporarily deenergizing alarm or control 61 and .64 during the starting of the arc heater and reenergizing these circuits a short time after arc start when steady state operation of the arc heater has been attained. Such circuitry may be required as otherwise, con trols 61 and .64 may prevent arc start.

It should further be noted that even though are heaters with two electrodes have been illustrated, the circuitry can as well be utilized between electrodes of opposing polarity of arc heaters using more than two electrodes.

Our invention is particularly useful with are heaters used in chemical processing. Where a feed stock hydrocarbon, for example methane, CH is pyrolyzed, carbon is deposited in an amount depending upon operating conditions, upon the wall or heat shield of the arc chamber. Ultimately, this carbon deposit becomes suflicient to form a conductive path for arc current.

Whereas relays 28 and are shown as direct current relays, suitable alternating current relays could be employed and rectifiers 23 and 46 respectively dispensed with.

It will be understood that other relay contact arrangements may be employed if desired.

It will be understood that both are heaters 10 and 36 have means symbolized by inlets 24 and 44 respectively, for admitting gas to be heated into the arc chamber thereof.

Nozzles 21 and 71 are symbolical; arc heaters 10 and 36 could have exhaust nozzles for heated gas located between electrodes if desired.

The circuits of both FIGS. 1 and 2 may include any convenient means, not shown, for adjusting the sensitivity of the circuits.

Whereas source 11 has been described as a cycle source, other power frequencies could be used and the LC values of 1816 accordingly changed.

The above-described drawing and the aforegoing written description are illustrative and exemplary only and are not to be interpreted in a limiting sense.

We claim as our invention:

1. Current path indicating apparatus for use with arc heater apparatus including an arc heater having at least a pair of spaced electrodes, means for admitting fluid to be heated to the arc chamber, means for exhausting heated fluid from the arc chamber, and a source of potential connected to the electrodes for normally producing and sustaining an arc between electrodes, the current path indicating apparatus including means for obtaining a signal while high frequency voltage variations are present in the voltage across the arc heater, said high frequency voltage variations resulting from the dynamic nature of the arc and not depending on material lost from an electrode producing a temporary path of less resistance and being present during normal operation while an arc is occurring between electrodes and ceasing when the arc current takes a path through any material and other than the normal arc-producing path, and signal utilization means connected to the signal obtaining means. 2. Apparatus according to claim 1 in which the current path other than the normal arc-producing path is provided by deposited conductive material on the inside wall of the arc chamber.

3. Apparatus according to claim 1 in which the current path other than the normal arc-producing path is provided by deposited carbon on the inside wall of the arc chamber.

4. Apparatus according to claim 1 in which the current path other than the normal arc-producing path is through inadequately electrically insulated structure of the arc heater.

5. In combination, an arc heater having at least a pair of spaced electrodes, means for admitting fluid into the arc chamber to be heated, and means for exhausting heated fluid from the chamber, the electrodes of said are heater being adapted to be connected to a source of potential for producing and sustaining an arc between electrodes, said arc heater being characterized by fluctuations in the range of several hundred to a thousand times per second resulting from normal arc instability and the dynamic nature of the are, said fluctuations occurring while the arc heater is operating normally and an arc is occurring between electrodes, and means operatively connected to the arc heater for utilizing the fluctuations in voltage for indicating whether the current from the source is producing an arc between electrodes and whether the current from the source is following some other path between electrodes.

6. Apparatus according to claim in which the other current path between electrodes is provided by deposited conductive material on the inside wall of the arc chamber.

7. Apparatus according to claim 5 in which the other current path between electrodes is provided by deposited carbon on the inside wall of the arc chamber.

8. Apparatus according to claim 5 in which the other current path between electrodes is through inadequately electrically insulated structure of the arc heater.

9. In arc heater apparatus according to claim 5 of the type employed in chemical processing where a deposit of conductive material may be formed in the arc heater and provide a path for current between electrodes, the arc heater having an alternating current source of predetermined power frequency not greater than several hundred cycles per second, the indicating means including highpass filter means operatively connected across the electrodes of the arc heater for passing frequencies greater than the power frequency of the source, rectifier means operatively connected to the filter means for rectifying the signal from the filter means, and relay means having a winding operatively connected to receive the output of the rectifier means, voltage fluctuations resulting from are instability and the dynamic nature of the are being passed by the filter means and rectified by the rectifier means and used to maintain the relay winding normally energized, the relay winding becoming deenergized when the arc current takes a path through the deposited conductive material.

10. Indicating means according to claim 9 including in addition voltage divider means between the filter means and the arc heater.

11. Indicating means according to claim 9 including in addition normally open contacts for the relay means, said contacts being closed when the winding is deenergized as a result of current in the arc heater taking a path through the deposited conductive material, an alarm and control device electrically connected to the relay contacts, and source means for energizing the alarm and control device when the relay winding is deenergized and a circuit through the contacts is completed.

.12. Apparatus according to claim 9 in which the alternating current source is additionally characterized as having a very low internal impedance compared to the open circuit impedance between electrodes of the arc heater.

13. In combination, an arc heater adapted for chemical processing, the arc heater being subject to the deposit of carbon on the wall thereof between electrodes, the arc heater being adapted to have a source of potential connected to the electrodes of the arc heater, the arc heater producing high frequency variations in the range of several hundred to a thousand times per second in the voltage applied thereto while the arc current is producing an arc path between electrodes, said high frequency voltage variations ceasing when the arc current takes a path through the deposit of carbon, and means connected to the arc heater for utilizing the high frequency voltage variations to give an indication of which path the current between electrodes is taking.

14. Apparatus according to claim 13 in which the means for utilizing the high frequency variations includes means for rectifying the high frequency variations to obtain a control signal, and signal responsive means having the control signal applied thereto.

15. Apparatus according to claim 13 including in addition means connected to the arc heater and normally energized by the high frequency voltage variations, said last-named means becoming deenergized when the are current takes a path through the carbon deposit and the high frequency variations cease.

16. In an arc heater apparatus according to claim 5, a direct current source normally sustaining the are between the electrodes.

17. In arc heater apparatus according to claim 5, an alternating current source having a frequency lower than the frequency of voltage fluctuations resulting from arc instability and the dynamic nature of the arc.

-18. Apparatus according to claim 16 wherein the indicating means includes rectifier means coupled to the arc heater for rectifying the high frequency voltage variations to obtain a direct current, and relay means having said last-named direct current applied thereto to maintain the relay means normally energized while the arc is operating normally.

19. Apparatus according to claim 18 including in addition alarm and control means electrically connected to the contacts of the relay means.

20. Apparatus according to claim 18 including voltage divider means operatively connected between the arc heater and the rectifier means.

2.1. Apparatus according to claim 18 including in addition capacitor means connected in shunt with the winding of the relay means.

22. Current path indicating apparatus according to claim 1 wherein the source of potential is an alternating current source of predetermined power frequency, and the signal obtaining means includes a high-pass filter for passing only frequencies higher than the power frequency.

23. Current path indicating apparatus according to claim 1 wherein the source of potential is a direct current source, and the signal obtaining means includes rectifier means coupled to the arc heater for rectifying the high frequency voltage variations.

24. Current path indicating apparatus according to claim 22 including in addition rectifier means connected to the high-pass filter means to receive the output thereof.

25. The method of monitoring an are produced by an alternating current of power frequency which comprises obtaining from the electrode terminals an alternating current signal having a frequency within the range of several hundred to a thousand cycles per second resulting from normal voltage fluctuations caused by the dynamic instability of the arc and in the absence of any material transfer between electrodes, separating from the signal the component of power frequency, and utilizing the remaining signal representing only the dynamic instability of the arc in normal operation to indicate proper arc operation.

26. The method according to claim 25 wherein a highpass filter is connected across the electrodes and the signal representing the dynamic nature of the arc is obtained as an output from the high-pass filter.

27. The method according to claim 26 including the step of rectifying the output of the high-pass filter to obtain a direct current indicating signal.

References Cited UNITED STATES PATENTS 2,027,224 1/1936 David 315-135 X 2,858,411 10/1958 Gage W 219- 3,121,675 2/1964 Case 260-679 X 3,318,791 5/1967 Harris et al. 260-679 X JOHN W. HUCKERT, Primary Examiner B. ESTRIN, Assistant Examiner US. Cl. X.R. 

